1. Field of the Invention
The present invention relates to a fuel cell stack formed by stacking fuel cells, each including an electrolyte electrode assembly and separators. The electrolyte electrode assembly includes a pair of electrodes, with an electrolyte interposed between the electrodes.
2. Description of the Related Art
For example, a polymer electrolyte fuel cell employs a membrane electrode assembly (electrolyte electrode assembly), which includes an anode, a cathode, and an electrolyte membrane interposed between the anode and the cathode. The electrolyte membrane is a solid polymer ion exchange membrane. The membrane electrode assembly and separators sandwiching the membrane electrode assembly therebetween make up a fuel cell.
Normally, several tens to hundreds of fuel cells are stacked together to form a fuel cell stack. It is necessary to accurately position the components of the fuel cell, while maintaining the fuel cells in alignment with each other accurately. In this regard, for example, a fuel cell as disclosed in Japanese Laid-Open Patent Publication No. 2004-172094 is known.
The fuel cell is formed by sandwiching an electrolyte electrode assembly between a first separator and a second separator. The electrolyte electrode assembly includes a pair of electrodes, with an electrolyte interposed between the electrodes. Each of the first and second separators includes first and second positioning holes. First and second insulating positioning members are fitted into the first and second positioning holes, and an outer wall of the second insulating positioning member is fitted in an inner wall of the first insulating positioning member in order to position the first and second separators while insulating the first and second separators.
Further, in a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2004-241208, a unit cell is formed by sandwiching an electrolyte electrode assembly between first and second separators, wherein the electrolyte electrode assembly includes a pair of electrodes with an electrolyte interposed between the electrodes. In the fuel cell, a plurality of metal clip members are provided for supporting outer ends of the first and second separators at a plurality of positions. Each of the metal clip members includes a side plate, and first and second tongues folded at ends of the side plate for holding the outer ends of the first and second separators. The first and second tongues are longer than the side plate, and have a certain elasticity.
For example, the fuel cell stack adopts a structure in which a tightening load is applied in a stacking direction, by means of tie rods that extend in the stacking direction of the fuel cells. Alternatively, the fuel cell stack adopts a structure in which a tightening load is applied in the stacking direction in a state in which the stacked fuel cells are placed within a box shaped casing. Normally, the fuel cell stack is used in an automobile, and is mounted in a vehicle.
Under these circumstances, for example, if an external load is applied to the vehicle, and the casing becomes deformed in a manner so as to contact the separators, short-circuiting of the separators may occur. In addition, the separators may become deformed, thus degrading the sealing performance of the fuel cells.